src/Runtime/TransitionSizeDistribution.cs (1)

17-27: Constructor change looks good; add invariant checks and make MinimumSize initialisation explicit

Dropping the ID simplifies usage. Please also guard inputs and set m_MinimumSize explicitly to avoid relying on default initialisation.

         public TransitionSizeDistribution(
             int? stratumId, int? iteration, int? timestep, 
             int transitionGroupId, double maximumSize, double relativeAmount)
         {
             this.m_StratumId = stratumId;
             this.m_Iteration = iteration;
             this.m_Timestep = timestep;
             this.m_TransitionGroupId = transitionGroupId;
-            this.m_MaximumSize = maximumSize;
-            this.m_RelativeAmount = relativeAmount;
+            if (maximumSize <= 0)
+            {
+                throw new ArgumentOutOfRangeException(nameof(maximumSize), "Maximum size must be > 0.");
+            }
+            if (double.IsNaN(relativeAmount) || relativeAmount < 0)
+            {
+                throw new ArgumentOutOfRangeException(nameof(relativeAmount), "Relative amount must be ≥ 0.");
+            }
+            this.m_MinimumSize = 0.0; // explicit default
+            this.m_MaximumSize = maximumSize;
+            this.m_RelativeAmount = relativeAmount;
         }

src/Runtime/STSimTransformer.Collections.cs (1)

2244-2275: Constructor call is correct; add defensive validation on row values before creating items

Prevent bad data from propagating (negative/zero sizes or amounts) and fail fast with a clear message tied to the datasheet.

             DataSheet ds = this.ResultScenario.GetDataSheet(Strings.DATASHEET_TRANSITION_SIZE_DISTRIBUTION_NAME);

             foreach (DataRow dr in ds.GetData().Rows)
             {
                 int? StratumId = null;
                 int? Iteration = null;
                 int? Timestep = null;
                 int TransitionGroupId = Convert.ToInt32(dr[Strings.DATASHEET_TRANSITION_GROUP_ID_COLUMN_NAME], CultureInfo.InvariantCulture);
                 double MaximumSize = Convert.ToDouble(dr[Strings.DATASHEET_TRANSITION_SIZE_DISTRIBUTION_MAXIMUM_AREA_COLUMN_NAME], CultureInfo.InvariantCulture);
                 double RelativeAmount = Convert.ToDouble(dr[Strings.DATASHEET_TRANSITION_SIZE_DISTRIBUTION_RELATIVE_AMOUNT_COLUMN_NAME], CultureInfo.InvariantCulture);
+                if (MaximumSize <= 0)
+                {
+                    throw new ArgumentException(ds.DisplayName + " -> Maximum area must be > 0.");
+                }
+                if (double.IsNaN(RelativeAmount) || RelativeAmount < 0)
+                {
+                    throw new ArgumentException(ds.DisplayName + " -> Relative amount must be ≥ 0.");
+                }

                 if (dr[Strings.DATASHEET_STRATUM_ID_COLUMN_NAME] != DBNull.Value)
                 {
                     StratumId = Convert.ToInt32(dr[Strings.DATASHEET_STRATUM_ID_COLUMN_NAME], CultureInfo.InvariantCulture);
                 }

                 if (dr[Strings.DATASHEET_ITERATION_COLUMN_NAME] != DBNull.Value)
                 {
                     Iteration = Convert.ToInt32(dr[Strings.DATASHEET_ITERATION_COLUMN_NAME], CultureInfo.InvariantCulture);
                 }

                 if (dr[Strings.DATASHEET_TIMESTEP_COLUMN_NAME] != DBNull.Value)
                 {
                     Timestep = Convert.ToInt32(dr[Strings.DATASHEET_TIMESTEP_COLUMN_NAME], CultureInfo.InvariantCulture);
                 }

                 TransitionSizeDistribution tsd = new TransitionSizeDistribution(
                     StratumId, Iteration, Timestep, TransitionGroupId, MaximumSize, RelativeAmount);